1. Field of the Invention
The present invention relates to a field sequential liquid crystal display apparatus.
2. Description of the Related Art
A field sequential liquid crystal display apparatus has a construction in which a liquid crystal layer is sandwiched between a pair of front and rear substrates. Electrodes are formed on the opposing inner surfaces of these substrates. This apparatus comprises a liquid crystal display device, a plurality of light-emitting elements, and an illuminating unit. The liquid crystal display device forms a plurality of display elements which control the transmission of a light beam in a region where the electrodes of the pair of front and rear substrates oppose each other. The light-emitting elements are arranged at the back of this liquid crystal display device and emit light beams having a plurality of unit colors (e.g., three colors of red, green, and blue). The illuminating unit allows these unit-color light beams emitted by the light-emitting elements to enter the liquid crystal display device from the back side. To display an arbitrary color by temporal color mixing of a plurality of unit colors in the apparatus having this configuration, unit-color image data signals corresponding to these unit colors are sequentially supplied to the liquid crystal display device in each field for displaying one of these unit colors. During the period of one frame composed of a plurality of continuous fields, equal in number to the unit colors, for sequentially displaying different unit colors, the unit-color image data are sequentially written in the display elements of the liquid crystal display device. In addition, in accordance with this sequential write of the unit-color image data, the light-emitting elements of the plurality of unit colors are sequentially turned on. In this way, a color image (full-color image or multi-color image) is displayed.
In this field sequential liquid crystal display apparatus, the liquid crystal display device need not be equipped with any color filter, so there is no color absorption by the color filter. Also, this apparatus displays a color image by sequentially writing unit-color image data into all the display elements of the liquid crystal display device. Therefore, the apparatus can display bright, high-resolution color images compared to a liquid crystal display apparatus in which color filters of a plurality of colors corresponding to individual display elements of a liquid crystal display device are alternately arranged.
In the above field sequential liquid crystal display apparatus, one frame for forming one image is made up of three fields which display three colors, red, green, and blue. That is, one field for displaying one color is ⅓ of one frame, so data corresponding to one color must be written in and displayed by the liquid crystal display device in one field. Therefore, the liquid crystal display device is required to have high-speed response characteristics.
Accordingly, as the liquid crystal display device used in the field sequential liquid crystal display apparatus, the use of a liquid crystal display device using a ferroelectric liquid crystal capable of high-speed response, or a liquid crystal display device having a liquid crystal layer in which liquid crystal molecules are bent, has been proposed.
Unfortunately, in the liquid crystal display device using a ferroelectric liquid crystal, it is difficult to obtain uniaxial alignment in which liquid crystal molecules are evenly aligned in one direction. In the liquid crystal display device having a liquid crystal layer in which liquid crystal molecules are bent, it is difficult to obtain a liquid crystal layer in which liquid crystal molecules are stably, evenly aligned. In either case, no liquid crystal display device having stable operating characteristics and high-speed response characteristics can be obtained.
Also, the field sequential liquid crystal display apparatus always displays a color image by sequentially writing unit-color image data into the display elements of the liquid crystal display device, and sequentially turning on a plurality of light-emitting elements of the illuminating unit in accordance with this data write. This increases the number of times of data write for causing the liquid crystal display device to display one image. Since this raises the field frequency and the frequency of each signal, the power consumption also increases.
It is an object of the present invention to provide a field sequential liquid crystal display apparatus using a liquid crystal display device having stable operating characteristics and high-speed response characteristics.
To achieve the above object, the present invention is achieved by the use of a liquid crystal display device having a liquid crystal layer which is sandwiched, with the liquid crystal molecules being aligned in one direction, between a pair of substrates having electrodes formed on them, and in which the tilt angle the liquid crystal molecules make with the substrates changes in accordance with an electric field applied between the electrodes, or by the use of a homogeneous type liquid crystal display device in which liquid crystal molecules are aligned in one direction.
It is another object of the present invention to provide a field sequential liquid crystal display apparatus capable of transmission display using a illuminating light beam from an illuminating unit of the display apparatus, and reflection display using external light from the external environment of a display device, and to provide a field sequential liquid crystal display apparatus which reduces the power consumption. This object can be achieved by placing a reflecting member on the side of a liquid crystal layer of the liquid crystal display device away from the side opposite to an observer, and using a controller capable of freely turning on and off the illuminating unit.
To achieve the above objects, a liquid crystal display apparatus according to a first aspect of the present invention comprises a liquid crystal display device including a pair of opposing substrates, electrodes formed to oppose each other on opposing inner surfaces of the pair of substrates, and a liquid crystal layer sandwiched between the pair of substrates with liquid crystal molecules being aligned in one direction, of which the tilt angle to the inner surfaces of the substrates changes in accordance with an electric field applied between the electrodes, in which a display element for controlling transmission of a light beam is formed by at least one region in which the electrodes oppose each other; an illuminating unit is placed on one side of the liquid crystal display device to display an arbitrary color by mixing a plurality of unit colors, the illuminating unit selectively emitting light beams having the plurality of unit colors and irradiating the liquid crystal display device with the light beams having the plurality of unit colors; and a controller sequentially supplies to the liquid crystal display device a plurality of display signals corresponding to the light beams having the plurality of unit colors emitted by the illuminating unit, in each period during which one unit color of the light beams having the plurality of unit colors is displayed, and which causes the illuminating unit to selectively emit a light beam having a unit color corresponding to the display signal in each period.
In this invention according to the first aspect, the liquid crystal display device of the field sequential liquid crystal display apparatus has the liquid crystal layer which is sandwiched with the liquid crystal molecules being aligned in one direction, and in which the tilt angle the liquid crystal molecules make with the substrates changes in accordance with an electric field applied between the electrodes. Since the structure of the liquid crystal layer is simple, the liquid crystal molecules are evenly and stably aligned. Consequently, stable operating characteristics and high-speed response characteristics can be obtained, and the fabrication is facilitated.
In this invention, the liquid crystal display device may have a homogeneously aligned nematic liquid crystal layer, as the liquid crystal layer, in which when no electric field is applied between the electrodes, liquid crystal molecules are substantially parallel to the surfaces of the substrates and pointed in one direction without being twisted. The liquid crystal display device may be a matrix type liquid crystal display device which comprises a plurality of pixel electrodes formed on one of opposing inner surfaces of opposing substrates, and at least one counterelectrode formed on the inner surface of the other substrate, and in which a plurality of pixel regions formed by regions where the pixel electrodes and the counterelectrode oppose each other are arranged in a matrix manner. Furthermore, the liquid crystal display device is desirably an active matrix display device which comprises a plurality of active elements formed on one substrate and connected in one-to-one correspondence with the plurality of pixel electrodes, a gate line for controlling operations of the active elements, and a data line which supplies a display data signal to the pixel electrodes via the active elements.
Also, in this invention, the controller may comprise a display device driver which, in order to display an arbitrary color by mixing a plurality of unit colors, sequentially supplies to the liquid crystal display device a plurality of unit-color image data signals corresponding to the plurality of unit colors in each field for displaying one of the plurality of unit colors, and sequentially writes the plurality of unit-color image data signals into the display elements of the liquid crystal display device during the period of one frame composed of a plurality of continuous fields for displaying different unit colors, and an illumination controller which selectively emits one of the plurality of unit colors in accordance with the sequential write of the unit-color image data performed for each frame by the display device driver. With this arrangement, color images and an image having one predetermined color can be displayed. Since unit-color image data is written for each frame, the write frequency lowers, and this reduces the power consumption.
In this invention, the display apparatus may further comprise a reflecting member which reflects a light beam, incident from one substrate of the liquid crystal display device and transmitted through the liquid crystal layer, toward the other substrate. This reflecting member is a semitransparent reflecting film formed between the liquid crystal layer of the liquid crystal display device and the illuminating unit, or a reflecting film formed on a side of the illuminating unit away from the liquid crystal display device. This arrangement enables reflection display using external light in the environment in which this liquid crystal display apparatus is placed. Since the illuminating unit is turned off in this reflection display, the power consumption is further reduced.
To achieve the above objects, a liquid crystal display apparatus according to a second aspect of the present invention comprises a liquid crystal display device which is formed by sandwiching a liquid crystal layer between a pair of front and rear substrates having opposing inner surfaces on which electrodes are formed, and which forms a plurality of display elements for controlling transmission of a light beam by regions where the electrodes of the pair of front and rear substrates oppose each other, a display device driver which, in order to display an arbitrary color by mixing a plurality of unit colors, sequentially supplies to the liquid crystal display device a plurality of unit-color image data signals corresponding to the plurality of unit colors in each field for displaying one of the plurality of unit colors, and sequentially writes the plurality of unit-color image data signals into the display elements of the liquid crystal display device during the period of one frame composed of a plurality of continuous fields for displaying different unit colors, an illuminating unit which has a plurality of light-emitting elements for emitting light beams having the plurality of unit colors, which is placed on the rear substrate side of the liquid crystal display device so as to allow the light beams emitted by the light-emitting elements to enter the liquid crystal display device from the rear substrate, and which can select sequential turn-on by which the light-emitting elements of the plurality of unit colors are sequentially turned on in accordance with the sequential write of the unit-color image data, and total turn-off by which all the light-emitting elements are turned off, and a reflecting member which reflects a light beam, incident from the front substrate of the liquid crystal display device and transmitted through the liquid crystal layer, toward the front substrate.
This invention according to the second aspect comprises the reflecting member which reflects a light beam transmitted through the liquid crystal layer of the liquid crystal display device toward the front substrate, and the illuminating unit capable of selecting sequential turn-on by which the light-emitting elements of the plurality of unit colors are sequentially turned on in accordance with the sequential write of the unit-color image data, and total turn-off by which all the light-emitting elements are turned off. By totally turning off this illuminating unit, therefore, it is possible to introduce external light in the environment in which the liquid crystal display apparatus is placed, and to display an image with this external light. This can reduce the power consumption.
In the liquid crystal display apparatus of this invention, the liquid crystal display device may comprise a homogeneously aligned nematic liquid crystal layer in which when no electric field is applied between the electrodes, liquid crystal molecules are aligned at a predetermined pretilt angle to surfaces of the substrates and pointed in one direction without being twisted. This liquid crystal display device may be an active matrix type liquid crystal display device which comprises a plurality of pixel electrodes formed on one of the opposing inner surfaces of the opposing substrates, and at least one counterelectrode formed on the inner surface of the other substrate, and in which a plurality of pixel regions formed by regions where the pixel electrodes and the counterelectrode oppose each other are arranged in a matrix manner.
In this invention, the reflecting member is preferably a semitransparent reflecting film formed between the liquid crystal layer of the liquid crystal display device and the illuminating unit. This makes both transmission display and reflection display possible.
In addition, the display device driver may have a black-and-white image data writing device which writes black-and-white image data into the display elements of the liquid crystal display device for each frame, and the illuminating unit has a total turn-on device which turns on all the light-emitting elements in accordance with a write of the black-and-white image data. This can lower the write frequency and hence reduce the power consumption. Also, the display device driver may have a black-and-white image data writing device which writes black-and-white image data into the display elements of the liquid crystal display device for each frame, and the illuminating unit has a total turn-off device which turns off all the light-emitting elements in accordance with a write of the black-and-white image data. Since black-and-white display can be performed by reflection type display and the write frequency can be lowered, the power consumption can be further reduced. Furthermore, the display device driver may have a monochromatic image data writing device which writes monochromatic image data for displaying a monochromatic image into the display elements of the liquid crystal display device for each frame, and the illuminating unit has a selective turn-on device which turns on at least one of the light-emitting elements having the plurality of colors in accordance with the write of the monochromatic image data. Since an image can be displayed in one predetermined color and the write frequency can be lowered, the power consumption can be further reduced.
To achieve the above objects, a liquid crystal display apparatus according to a third aspect of the present invention comprises a liquid crystal display device which is formed by sandwiching a liquid crystal layer between a pair of front and rear substrates having opposing inner surfaces on which electrodes are formed, and which forms a plurality of display elements for controlling transmission of a light beam by regions where the electrodes of the pair of front and rear substrates oppose each other, a display device driver having a unit-color image data writing device which, in order to display an arbitrary color by mixing a plurality of unit colors, sequentially supplies to the liquid crystal display device a plurality of unit-color image data signals corresponding to the plurality of unit colors for each field for displaying one of the plurality of unit colors, and sequentially writes the plurality of unit-color image data into the display elements of the liquid crystal display device during the period of one frame composed of a plurality of continuous fields for displaying different unit colors, and a monochromatic image data writing device which writes monochromatic image data for displaying an image in one predetermined color into the display element of the liquid crystal display device for each frame, an illuminating unit which has a plurality of light-emitting elements for emitting light beams having the plurality of unit colors, is placed on the rear substrate side of the liquid crystal display device so as to allow the light beams emitted by the light-emitting elements to enter the liquid crystal display device from the rear substrate, and can select sequential turn-on by which the light-emitting elements of the plurality of unit colors are sequentially turned on in accordance with a sequential write of the unit-color image data, and selective turn-on by which a light-emitting element of at least one unit color, of the plurality of light-emitting elements, which corresponds to the one predetermined color is turned on in accordance with a write of the monochromatic image data.
In this invention according to the third aspect, the display device driver comprises the monochromatic image data writing device which writes monochromatic image data for displaying an image in one predetermined color into the display elements of the liquid crystal display device, and the illuminating unit can perform selective turn-on by which at least one of the plurality of light-emitting elements which has a unit color corresponding to the one predetermined color is turned on. Since the write frequency can be lowered, the power consumption can be reduced.
In this invention, the display device driver may further have a black-and-white image data writing device which writes black-and-white image data into the display elements of the liquid crystal display device for each frame, and the illuminating unit may further have a total turn-on device which turns on all the light-emitting elements in accordance with a write of the black-and-white image data. Since black-and-white images can also be displayed and the write frequency can be lowered, the power consumption can be further reduced. Also, the liquid crystal display apparatus may further comprise a reflecting member which reflects a light beam, incident from the front side of the liquid crystal display device and transmitted through the liquid crystal layer, toward the front side, and the illuminating unit has a total turn-off device which turns off all the light-emitting elements. This arrangement makes reflection type display feasible. Since the illuminating unit is totally turned off in this reflection display, the power consumption can be further reduced.
Furthermore, the liquid crystal display device may have an arbitrary pattern display area which displays an arbitrary display pattern, and a fixed pattern display area which displays a fixed display pattern, and the illuminating unit comprises a first illuminating device which faces the arbitrary pattern display area of the liquid crystal display device, and a second illuminating device which faces the fixed pattern display area of the liquid crystal display device, at least the first illuminating device comprising a plurality of light-emitting elements which emit a plurality of unit colors. With this arrangement, one display screen can be divided into a plurality of areas, and only a necessary area can be efficiently illuminated. This can further reduce the power consumption. In this case, the first illuminating device comprises a first light guiding plate which has an exit surface which faces the arbitrary pattern display area of the liquid crystal display device and an incident end face on which a light beam of a light source is incident, and a light source which opposes the incident end face of the first light guiding plate, the second illuminating device comprises a second light guiding plate which has an exit surface which faces the fixed pattern display area of the liquid crystal display device and an incident end face on which a light beam of a light source is incident, and a light source which opposes the incident end face of the second light guiding plate, and at least the light source of the first illuminating device comprises a plurality of light-emitting elements which emit a plurality of unit colors. This arrangement is favorable in decreasing the thickness of the illuminating unit and decreasing the size of the liquid crystal display apparatus.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.